Methods of operating a refrigeration system

Abstract

Methods of monitoring the operation of a refrigeration system, including interlocking the selection and operation of an engine and electric motor which are arranged to alternatively function as prime movers for a refrigerant compressor; detecting slippage of a clutch connected between the engine and compressor; and, detecting improper rotational direction of an evaporator fan motor. The interlocking method prevents energization of the drive motor while the engine is operative, and it includes monitoring engine oil pressure and engine RPM. The clutch slippage method includes detecting engine speed fluctuations and the polarity of battery current. The monitoring of the evaporator fan motor, which drives a fan which draws return air RA from a conditioned space, and discharges conditioned air DA into the conditioned space, includes the steps of comparing the difference between the temperatures RA and DA of the return air and discharge air with a predetermined reference value.

I claim: 
     
       1. A method of interlocking the selection and operation of an internal combustion engine and an electric drive motor which are arranged to selectively and alternatively function as a prime mover for a refrigerant compressor in a refrigeration system, to prevent energization of the electric motor while the engine is operative, comprising the steps of: monitoring engine oil pressure,   detecting the selection of the drive motor as the prime mover,   determining if the engine oil pressure is zero in response to said detecting step finding selection of the drive motor as the prime mover,   preventing energization of the drive motor, when de-energized, and de-energizing the drive motor, when energized, in response to the determining step finding the engine oil pressure is not zero,   initiating a predetermined timing period in response to the determining step finding the engine oil pressure is not zero,   repeating periodically the step of determining if the engine oil pressure is zero,   and providing an indication of a fault when the repeated determining step consistently finds the engine oil pressure is not zero over the predetermined timing period.   
     
     
       2. The method of claim 1 including the step of providing control means which must be energized to operate either the internal combustion engine or the drive motor, and wherein the step of preventing energization of the drive motor, and the step of de-energizing the drive motor, each include the step of de-energizing said control means. 
     
     
       3. The method of claim 1 including the steps of: determining if the speed of the internal combustion engine is zero in response to a finding that the engine oil pressure is zero,   preventing energization of the drive motor, when de-energized, and de-energizing the drive motor, when energized, in response to the determining step finding that the engine speed is not zero,   initiating a predetermined timing period in response to the determining step finding that the engine speed is not zero   repeating periodically the step of determining if the engine speed is zero,   and providing an indication of a fault when the repeated determining step consistently finds the engine speed is not zero over the predetermined timing period.   
     
     
       4. The method of claim 3 including the step of providing control means which must be energized to operate either the internal combustion engine or the drive motor, and wherein the step of preventing energization of the drive motor, and the step of de-energizing the drive motor, each include the step of de-energizing said control means. 
     
     
       5. The method of claim 3 including the step of permitting energization of the drive motor after the determining steps find that: (1) the engine oil pressure is zero, and (2) the engine speed is zero. 
     
     
       6. The method of claim 1 wherein the refrigeration system includes evaporator air mover means driven by an electric fan motor which draws return air from a conditioned space and discharges conditioned air into the conditioned space, including the steps of: energizing the fan motor,   detecting the temperatures RA and DA of the return air and the discharge air DA, respectively,   determining the difference between the temperatures RA and DA to provide a first difference value ΔD,   comparing said first difference value ΔD with a first reference value,   initiating a predetermined timing period in response to said first difference value ΔD exceeding said first reference value,   repeating, periodically, the steps of detecting the temperatures RA and DA of the return air and the discharge air, and the step of determining the difference between the temperatures RA and DA, to provide updated difference values ΔD,   comparing each of said updated difference values--ΔD with a second reference value,   and shutting the prime mover and fan motor down when the step of comparing each updated difference value ΔD with the second reference value consistently finds that each updated difference value ΔD exceeds said second reference value over said predetermined timing period.   
     
     
       7. The method of claim 6 wherein the first and second reference values have substantially the same magnitudes. 
     
     
       8. The method of claim 6 including the step of providing a fault indication in response to the step of shutting the prime mover and fan motor down, identifying improper rotational direction of the fan motor as cause of the shutdown. 
     
     
       9. The method of claim 1 including the steps of: providing a clutch between the internal combustion engine and refrigerant compressor,   and detecting slippage of the clutch while the internal combustion engine is the selected prime mover.   
     
     
       10. The method of claim 9 including the steps of providing an alternator driven by rotation of the compressor, and a battery connected to be charged by the alternator, and wherein the step of detecting slippage of the clutch includes the steps of: detecting a predetermined fluctuation in the speed of the internal combustion engine, when the internal combustion engine is the selected prime mover,   monitoring the polarity of the battery current, with a first polarity indicating battery charging current, and a second polarity indicating battery discharging current,   and shutting the internal combustion engine down in response to: (1) the detecting step detecting said predetermined fluctuation in engine speed, and (2) the monitoring step detecting the second polarity.   
     
     
       11. The method of claim 10 wherein the step of detecting the predetermined fluctuation in engine speed includes the steps of detecting a predetermined change in the magnitude of the engine speed, in a predetermined direction, over a predetermined period of time. 
     
     
       12. The method of claim 10 including the steps of: providing a fault indication in response to the step of shutting the internal combustion engine down,   and identifying the clutch as the cause of engine shutdown.   
     
     
       13. The method of claim 10 wherein the step of detecting a predetermined fluctuation in the speed of the internal combustion engine includes the steps of: monitoring engine speed,   providing a first speed value,   initiating a predetermined timing period after the step of providing the first speed value,   providing a second speed value after the expiration of the predetermined timing period,   and comparing the second speed value with a sum value obtained by adding a predetermined reference value to the first speed value,   with the predetermined fluctuation being indicated when the comparing step finds the second speed value exceeds said sum value.   
     
     
       14. The method of claim 10 wherein the step of detecting a predetermined fluctuation in the speed of the internal combustion engine includes the steps of: monitoring engine speed,   providing a first speed value,   initiating a predetermined timing period after the step of providing the first speed value,   providing a second speed value after the expiration of the predetermined timing period,   and comparing the second speed value with a difference value obtained by subtracting a predetermined reference value from the first speed value,   with the predetermined fluctuation being indicated when the comparing step finds the second speed value is less than said difference value.   
     
     
       15. The method of claim 10 including the steps of: counting the number of predetermined fluctuations in engine speed to provide a count value, when the monitoring step detects the first polarity,   initiating a predetermined timing period in response to a count value of one,   shutting down the internal combustion engine in response to the count value reaching a predetermined reference value before the expiration of said predetermined timing period,   and resetting the count value to zero in response to the expiration of said predetermined timing period before the count value reaches said predetermined reference value.   
     
     
       16. The method of claim 15 wherein the step of detecting the predetermined fluctuation in engine speed includes the steps of detecting a predetermined speed change magnitude, in a first predetermined direction, over a predetermined period of time, to provide a first predetermined fluctuation, and further detecting a predetermined speed change magnitude, in a direction opposite to said first predetermined direction, over a predetermined period of time, to provide a second predetermined fluctuation, and incrementing the count value in response to the detection of either of said first and second predetermined fluctuations. 
     
     
       17. The method of claim 10 wherein the step of detecting a predetermined fluctuation in the speed of the internal combustion engine includes the step of providing an engine speed sensor, and further including the steps of: detecting when the engine speed sensor is faulty,   and shutting the internal combustion engine down after: (1) the detecting step indicates the engine speed sensor is faulty, and (2) the monitoring step detects the second polarity.   
     
     
       18. The method of claim 17 including the step of initiating a predetermined timing period, prior to the step of shutting the internal combustion engine down, in response to the monitoring step detecting the second polarity, and repeating periodically the monitoring step over said predetermined timing period, with the step of shutting the internal combustion engine down being initiated at the expiration of said predetermined timing period when the repeated monitoring step consistently detects the second polarity over said predetermined timing period. 
     
     
       19. The method of claim 17 including the steps of: providing a fault indication, in response to the step of shutting the internal combustion engine down,   and identifying the alternator as the cause of shutdown.   
     
     
       20. A method of detecting slippage of a clutch disposed between an internal combustion engine and a refrigerant compressor in a refrigeration system in which a prime mover for the compressor is selectable between the internal combustion engine and clutch, and an electric drive motor, and wherein the refrigeration system further includes an alternator driven by rotation of the compressor, and a battery connected to be charged by the alternator, comprising the steps of: detecting a predetermined fluctuation in the speed of the internal combustion engine, when the internal combustion engine is the selected prime mover,   monitoring the polarity of the battery current, with a first polarity indicating battery charging current, and a second polarity indicating battery discharging current,   and shutting the internal combustion engine down in response to: (1) the detecting step detecting said predetermined fluctuation in engine speed, and (2) the monitoring step detecting the second polarity.   
     
     
       21. The method of claim 20 wherein the step of detecting the predetermined fluctuation in engine speed includes the steps of detecting a predetermined change in the magnitude of the engine speed, in a predetermined direction, over a predetermined period of time. 
     
     
       22. The method of claim 20 including the steps of: providing a fault indication in response to the step of shutting the internal combustion engine down,   and identifying the clutch as the cause of engine shutdown.   
     
     
       23. The method of claim 20 wherein the step of detecting a predetermined fluctuation in the speed of the internal combustion engine includes the steps of: monitoring engine speed,   providing a first speed value,   initiating a predetermined timing period after the step of providing the first speed value,   providing a second speed value, after the expiration of the predetermined timing period,   and comparing the second speed value with a sum value obtained by adding a predetermined reference value to the first speed value,   with the predetermined fluctuation being indicated when the comparing step finds the second speed value exceeds said sum value.   
     
     
       24. The method of claim 20 wherein the step of detecting a predetermined fluctuation in the speed of the internal combustion engine includes the steps of: monitoring engine speed,   providing a first speed value,   initiating a predetermined timing period after the step of providing the first speed value,   providing a second speed value, after the expiration of the predetermined timing period,   and comparing the second speed value with a difference value obtained by subtracting a predetermined reference value from the first speed value,   with the predetermined fluctuation being indicated when the comparing step finds the second speed value is less than said difference value.   
     
     
       25. The method of claim 20 including the steps of: counting the number of predetermined fluctuations in engine speed to provide a count value, when the monitoring step detects the first polarity,   initiating a predetermined timing period in response to a count value of one,   shutting down the internal combustion engine in response to the count value reaching a predetermined reference value before the expiration of said predetermined timing period,   and resetting the count value to zero in response to the expiration of said predetermined timing period before the count value reaches said predetermined reference value.   
     
     
       26. The method of claim 25 wherein the step of detecting the predetermined fluctuation in engine speed includes the steps of detecting a predetermined speed change magnitude, in a first predetermined direction, over a predetermined period of time, to provide a first predetermined fluctuation, and further detecting a predetermined speed change magnitude, in a direction opposite to said first predetermined direction, over a predetermined period of time, to provide a second predetermined fluctuation, and incrementing the count value in response to the detection of either of said first and second predetermined fluctuations. 
     
     
       27. The method of claim 20 wherein the step of detecting a predetermined fluctuation in the speed of the internal combustion engine includes the step of providing an engine speed sensor, and further including the steps of: detecting when the engine speed sensor is faulty,   and shutting the internal combustion engine down after: (1) the detecting step indicates the engine speed sensor is faulty, and (2) the monitoring step detects the second polarity.   
     
     
       28. The method of claim 27 including the step of initiating a predetermined timing period, prior to the step of shutting the internal combustion engine down, in response to the monitoring step detecting the second polarity, and repeating periodically the monitoring step over said predetermined timing period, with the step of shutting the internal combustion engine down being initiated at the expiration of said predetermined timing period when the repeated monitoring step consistently detects the second polarity over said predetermined timing period. 
     
     
       29. The method of claim 27 including the steps of: providing a fault indication, in response to the step of shutting the internal combustion engine down,   and identifying the alternator as the cause of shutdown.   
     
     
       30. A method of detecting reverse operation of an evaporator fan motor in a refrigeration system having a refrigerant compressor driven by a prime mover, with the evaporator fan motor driving air mover means which draws return air from a conditioned space and discharges conditioned air into the conditioned space, including the steps of: detecting the temperatures RA and DA of the return air and the discharge air, respectively,   determining the difference between the temperatures RA and DA to provide a first difference value ΔD,   comparing said first difference value ΔD with a first reference value,   initiating a predetermined timing period when said first difference value ΔD exceeds said first reference value,   repeating, periodically, the steps of detecting the temperatures RA and DA of the return air and the discharge air, and the step of determining the difference between the temperatures RA and DA, to provide updated difference values ΔD,   comparing each of said updated difference values--ΔD with a second reference value,   and shutting the prime mover and fan motor down when the step of comparing each updated difference value ΔD with the second reference value consistently finds that each updated difference value ΔD exceeds said second reference value over said predetermined timing period.   
     
     
       31. The method of claim 30 wherein the first and second predetermined reference values have substantially the same magnitudes. 
     
     
       32. The method of claim 30 including the step of providing a fault indication in response to the step of shutting the prime mover and the fan motor down, identifying improper rotational direction of the fan motor as the cause of the shutdown.